1. Field of the Invention
This invention relates in general to wheel line irrigation systems; particularly to dropped line systems; and even more particularly to systems with self leveling sprinklers.
2. Description of the Prior Art
Wheel line irrigation systems are well known in the art and are widely used in arid parts of the country for sprinkler irrigation of large areas. A conventional wheel line system includes a series of laterally spaced wheels which carry an irrigation pipeline, on the top of which are mounted a series of sprinklers; each sprinkler operable to cover a circular area of 60 feet in diameter, or an area of approximately 2,826 square feet. The sprinklers are placed 40 feet apart for overlap. The wheel line may be manually moved or self propelled.
Also in the art is a sprinkler of high volume and long reach known under the registered trademark as BIG GUN.RTM.. Such a sprinkler is of the rotary, arm-impact type having a nozzle discharge port of 0.5" or larger. Because of the water demand for such a sprinkler; the torque placed on the pipeline by reactive thrust; and oscillations due to the impact of the high pressure, high volume stream on the impact arm, the sprinkler is presently located only at the terminal outlet end of a conventional sprinkler system, closely adjacent to a support wheel. Mounting of such a sprinkler elsewhere on the pipeline causes destruction of the line because of the effect of the torque and oscillation on the line. The BIG GUN.RTM. type of sprinkler covers a circular area of 250 feet in diameter, or an area of approximately 49,000 square feet--some 17 times the area of conventional sprinklers. U.S. Pat. No. 4,700,897, issued to Alvin, Daren, and Reed Smith, provides an irrigation system in which high volume, large coverage sprinklers may be used. The Smith device, however, includes sprinklers mounted directly on the dropped line portion of the pipeline. In that the ground contour may be uneven and in that the sprinklers are fixed in position, the sprinklers may be in such an angle relative to ground so as to impact the ground causing erosion of the soil while, at the same time, not providing adequate coverage of the land to be irrigated.
U.S. Pat. No. 3,045,922, issued to A. E. Jensen, discloses a self leveling system utilizing a stub pipe to position the sprinkler from a horizontally extending pipeline so that the sprinkler can revolve about the pipeline in planetary fashion. Such self leveling structure cannot be used with high volume, long reach sprinklers, due to the high relative thrust and oscillations due to the impact of the high pressure stream on the impact arm. The Jensen device is also not suitable for high volume sprinklers in having a sprinkler connected to the main line by only a single pivot; and in having a sprinkler having a nozzle intake port which must be located above the longitudinal axis of the main line.